1. Field of the Invention
This invention relates to a spindle-motor control method, spindle-motor control device, spindle-motor drive circuit and disk device for controlling the rpm of a spindle motor, and more particularly to a spindle-motor control method, spindle-motor control device, spindle-motor drive circuit and disk device that are suitable for application in the control of a spindle motor that rotates a disk medium.
2. Description of the Related Art
Spindle motors are widely used as rotation drive. For example, disk drives that read or read/write data stored on a disk have a spindle motor for rotating the disk medium. When bringing this kind of spindle motor from the stopped state or low-speed rotation state to a target rpm(rotation speed), it is necessary to bring it to the target rpm quickly.
Devices that have spindle motors are used in a wide range of fields. Here, an example of a magneto-optical memory storage device, used as an external memory storage device for a computer, is explained. In a magneto-optical storage device, a magneto-optical medium is used for storing data. This medium has a substrate and a recording layer made of magnetic material that is formed on the substrate. This medium stores information by utilizing the change in heat and magnetic field caused by light.
There is a data track on this medium for recording and reproducing the data. Generally, a spiral shaped groove (tracking groove) is formed on the top of the substrate of the disk medium. The recording/reproduction track for data is formed on the land between grooves.
The optical beam from an optical head tracks this track. Information is recorded on the track during recording by using the change in heat and magnetic field caused by light. Moreover, when reproducing the information, the magneto-optical effect is used to reproduce the information from the reflected light of the light beam.
To record or reproduce information on the optical disk medium, it is necessary to constantly rotate the optical disk medium. A spindle motor is used to do this. A brushless motor is used as this spindle motor.
When the rotation precision of this spindle motor is not sufficient, tracking of the laser beam on the disk medium becomes unstable, and also becomes cause of error when recording or reproducing information on the disk medium. Therefore, it is necessary to maintain stable high-speed rotation.
PLL (Phase Locked Loop) control (phase synchronization control) has been used as a prior motor-rotation control method for maintaining stable rotation precision. In this system, the phase of the oscillation pulse of a liquid-crystal oscillator is compared with the rotation pulse (FG) that is generated when the motor rotates, to obtain the phase difference. This phase difference is stored in the charge pump, and then its waveform is adjusted to obtain a rotation-error signal. This rotation-error signal becomes the drive current for the motor. This makes it possible to obtain rotation with stable rotation precision. In this system, in order to improve the rotation jitter characteristics during steady rotation of the motor, the response characteristic of the charge pump is set to be slow.
However, the prior art has the following problems.
For example, in the magneto-optical disc device described above, the optical medium is loaded into the device. When doing this, the spindle motor is in the stopped state. After the disk medium has been mounted, the spindle motor is started. After the spindle motor has started and reached steady rotation, initial processing and tracking-servo processing are performed to match the characteristics of the mounted medium. The loading process is then completed and the device is in the ready state. However, in recent years, as a way of improving the data transfer rate, there is trend to increase the rpm of the spindle motor. When the rpm is increased, the amount of time required from start up until reaching steady rpm becomes longer. This increases the time required by the loading process from when the medium is mounted until the device is capable of an external interface (SCSI/ATAPI IF), and thus there is a possibility of a timeout error with the interface.
Magneto-optical memory storage devices are widely used as compact, external memory devices for personal computers. In this case, it is necessary to decrease the power consumption of the device. Therefore, a sleep function is used in order to reduce the power consumption and to prevent damage (changes in device over time or in medium characteristics) due to a rise in temperature. For example, when there is no access for a certain amount of time or more, then the following operation of the track stops, light emission from the laser diode stops, rpm of the spindle motor drops or stops. In addition, when a command for accessing the disk medium is received, it is necessary that the device quickly return to the ready state. In other words, when the spindle motor is stopped, or when rotation is locked in at an rpm that is slower than the steady rpm, it is necessary that the spindle motor is started quickly and that rotation is quickly brought to an rpm that will allow access of the medium.
A problem occurs however, in that the loading time or ready time become slower as the steady rpm of the spindle motor becomes faster.
In the PLL circuit of a prior spindle motor, in order to improve the rotation jitter characteristics at steady rotation of the spindle motor, the response characteristic of the charge pump is set to be slower. Therefore, when the rpm of the spindle motor is increasing, there is large overshoot, and a problem occurs in that it is not possible to reduce the time required after start up for rotation to become steady at the target rpm.
Conversely, when the response characteristic of the charge pump is set to be fast, the rotation jitter characteristic of the spindle motor at steady rotation decreases, and fluctuation in rotation occur at steady rotation.
In view of the problems described above, the object of this invention is to provide a spindle-motor control method, spindle-motor control device, and spindle-motor drive circuit for reducing the time from when the spindle mode is stopped or rotating at low speed until it reaches a target speed.
Another objective of the invention is to provide a spindle-motor control method, spindle-motor control device, and spindle-motor drive circuit for reducing the rise time of the spindle motor while maintaining the rotation precision at a constant rpm.
A further objective of the invention is to provide a spindle-motor control method, spindle-motor control device, and spindle-motor drive circuit for reducing the amount of overshoot that occurs during the rise time of the spindle motor.
The spindle-motor control method of this invention comprises: a step of detecting an actual speed of the spindle motor, a step of extracting a difference between a target speed and the actual speed, a step of charging a charge pump with that difference, a step of driving the spindle motor according to the charge amount, a step of detecting when the actual speed of the spindle motor reaches near the target speed, and a step of discharging the charge pump for a prescribed time according to the detection.
In this feature of the invention, the overshoot during the rise time is suppressed by discharging the difference that is stored in the charge pump. To control this overshoot, when it is detected that the actual speed of the spindle motor has reached near the target speed, the charge pump discharges for a prescribed amount of time. This makes it possible to control the amount of overshoot.
Moreover, since the response characteristic of the charge pump is not changed, it is possible to stably maintain rotation at the target speed.
In another feature of the invention, the aforementioned arrival detection step comprises a step of detecting when the actual speed of the spindle motor reaches the near the target speed after the spindle motor has been started.
This makes it possible to reduce the rise time to the target rpm when starting the spindle motor from the stopped state.
In another feature of the invention, the aforementioned arrival detection step comprises a step of detecting when the actual speed of the spindle motor has arrived at near the target high-speed speed after an instruction has been given for the spindle motor, rotating at low speed, to rotate at high speed.
Another feature of the invention further comprises a step of learning the prescribed time for performing the aforementioned discharge. This makes it possible to automatically obtain a discharge time that will minimize the rise time.
Another feature of the invention further comprises a step of setting a prescribed time for performing the aforementioned discharge according to the surrounding temperature. By setting the discharge time according to the surrounding temperature, it is possible to reduce the rise time regardless of changes in the surrounding temperature.
Another feature of the invention further comprises a step of setting a prescribed time for performing the aforementioned discharge according to the power-supply voltage. By setting the discharge time according to the power-supply voltage, it is possible to reduce the rise time regardless of changes in the power-supply voltage. This is especially useful when using a battery-driven device.
The spindle-motor control device of this invention comprises: a detection means for detecting the actual speed of the spindle motor; a drive circuit for extracting the difference between the target speed and the actual speed, charging the charge pump with this difference and driving the spindle motor according to the charge amount; and a control circuit for detecting when the actual speed of the spindle motor arrives near the target speed and discharging the charge pump for a prescribed time.
In this feature of the invention, the overshoot during the rise time is controlled by discharging the difference amount that is stored in the charge pump. To control this overshoot, when it is detected that the actual rpm of the spindle motor has reached near the target rpm, the charge pump discharges for a prescribed amount of time. This makes it possible to control the amount of overshoot.
Moreover, since the response characteristic of the charge pump is not changed, it is possible to stably maintain rotation at the target rpm.
In another feature of the spindle-motor control device of this invention, the charge pump comprises a discharge circuit operated by the control circuit and for discharging the charge pump. Since there is a discharge circuit, it is possible to easily discharge the charge pump.
In another feature of the spindle-motor control device of this invention, the aforementioned discharge circuit is operated by the tri-state buffer of the control circuit. With this it is not necessary to have a special switch for operating the discharge circuit.
In another feature of the spindle-motor control device of this invention, the aforementioned discharge circuit comprises a switch that is operated by the control circuit. This makes it possible to operate the discharge from a port of the control circuit.
The spindle-motor drive circuit of this invention comprises an extraction circuit for extracting the difference between the target rpm and the actual rpm of the spindle motor, a charge pump that is charged with this difference, and a drive circuit for generating a drive signal for the spindle motor according to the amount of charge of the charge pump, wherein the charge pump is operated externally and comprises a discharge circuit for discharging the charge pump.
By discharging the difference stored in the charge pump, it possible to control the overshoot during the rise time. Moreover, it is possible to operate the drive circuit externally, and the control circuit can easily operate the discharge. Furthermore, since the response characteristic of the charge pump is not changed, it is possible to stably maintain rotation at the target rpm.
The disk device of this invention comprises the aforementioned spindle-motor drive circuit. This makes it possible to reduce the time from when the start-up command is received until the disk is brought to steady rotation, as well as reduce the time required for the loading process.